1. Field of the Invention
This invention relates to an environmentally safe process for the production of a usable or storable product with a low susceptibility to elutriation by water. This product is produced from residues containing halides obtained from a waste gas cleaning process. The halide containing residues, as components of a crude dust having a CaO/SiO.sub.2 ratio between about 1.7 and about 3.4, are subjected to a thermal treatment for the production of chlorosilicates, and the gas produced during the thermal treatment process is subjected to at least one cleaning stage.
2. Background of the Invention
Residues from waste gas cleaning apparatus of waste incineration plants can contain high amounts of halogens, especially if the treatment process is a dry or semi-dry process. In this respect, the amount of chloride can be 20% or more and the gas can also contain some fluorides.
In general, the gas cleaning stage involves a sorption method on Ca(OH).sub.2 in which HCl, SO.sub.2, SO.sub.3, and HF, if present in the exhaust gases, can react so that the residue from the gas cleaning can contain basic chlorides - CaCl.sub.2 .multidot.Ca(OH).sub.2 .multidot.nH.sub.2 O, calcium chlorides - CaCl.sub.2 .multidot.nH.sub.2 O, anhydrous CaSO.sub.4, half hydrated CaSO.sub.4 .multidot.1/2H.sub.2 O, gypsum - CaSO.sub.4 .multidot.2H.sub.2 O, and fluorite - CaF.sub.2.
In addition, the adsorption material, Ca(OH).sub.2 can become carbonated at least partially to form CaCO.sub.3 because of the high CO.sub.2 content of the waste gases, and it will also generally become contaminated from ash particles in the waste gas. Thus, the residues, which residues contain the adsorption material, may also contain various amounts of calcium alumino silicates, alkali alumino silicates, iron oxides, iron hydroxides, and volatile heavy metals such as lead, zinc and copper.
Such residues are generally not usable as aggregates in concrete or street construction because of their heavy metal content and high chloride content, especially since most chloride compounds are readily susceptible to elutriation by water.
As disclosed by Federal Republic of Germany Patent DE 39 06 617, the components which can be leached out of the finished product are incorporated in a mineral matrix so that, compared to untreated residues containing halides from waste gas cleaning, a clearly lower susceptibility to elutriation by water is achieved. The residues are thereby converted into a product which can be used as a hydraulic binder or cement.
Such treatment is achieved by thermally treating the halogen containing residues as components of a crude dust or raw meal having a CaO/SiO.sub.2 ratio within a range of about 1.7 to 3.4 to thereby form chlorosilicates which have a low susceptibility for elutriation by water.
However, it has been determined that during the thermal treatment for the production of chlorosilicates, according to the process disclosed by DE 39 06 617 C1, the waste gases that are produced from the process also contain certain quantities of halides. The halides in this waste gas come from evaporation during the combustion process, and can account for up to about 10% of the total halide content of the pellets. This quantity of volatile halides therefore casts doubt on the utility of the process disclosed in DE 39 06 617 C1, to the extent that, on account of the air pollution laws, such large quantities of halides cannot simply be discharged into the atmosphere. An additional waste gas cleaning step for cleaning the waste gas is therefore necessary to meet pollution law standards when the process for making the chlorosilicates as disclosed by DE 39 06 617 C1, is being used.